1. Field of the Invention
The present invention relates to the field of microprocessor based computer systems. More specifically, the present invention relates to the packaging of high performance microprocessors on daughter cards.
2. Background Information
Historically, when microprocessor was first commercialized, each microprocessor held less than one million transistors, and operated at speeds below 20 MHz. Typically, the microprocessors were either solder mounted onto the motherboards directly or mounted to the motherboards through sockets. They were typically air cooled, and air flow was typically sustained by a system fan. Electromagnetic interference (EMI) and/or electrostatic discharge (ESD) shielding were not much of a concern.
In the pursuing years, the number of transistors packed into each microprocessor, as well as its operating speed have increased dramatically, especially in recent years. Correspondingly, the amount of heat that needs to be dissipated, as well as the amount of EMI emissions that needs to be absorbed and sensitivity to ESD during operation have increased. As a result, most of today's microprocessor based computer systems employ either local fans and/or heat sinks to help ensure that the microprocessors will run cool. At the same time, increased attentions have also been given to the design of system chassis to ensure the EMI emission absorption and ESD requirements are met.
This trend of increased transistor density and operating speed is expected to continue without any abatement. By the end of this year, it is expected that a typical desktop computer system will be powered by a microprocessor packing well over five million transistors, and operating in speeds in excess of 200 MHz. It is expected that because of the amount of heat needs to be dissipated, the precision of bonding between the processor and heat sink will reach a point of critical importance to ensure the processor will be cooled properly during operation. It is also expected that the size of the heat sink required for any one of these processors will be increased to a point that the spatial constraints imposed by the various de-facto system chassis form factors' must be addressed. In other words, it is unlikely that one heat sink will work (size-wise) for the various de-facto system chassis. At the same time, it is expected that the present system chassis based solution for EMI emission and/or ESD containment will no longer be adequate.
The heat sink problem is a dilemma for processor manufacturers. On one hand, because of the critical importance of the precision of bonding between a processor and a heat sink, a processor manufacturer cannot simply leave the job of bonding heat sinks to these high performance processors to the OEMs. However, if the processor manufacturers were to shoulder the burden of bonding the heat sinks, under the prior art, in addition to the burden of having to deal with yet another increase in heat sink size, the new burden of having to have multiple versions of heat sinks for one processor, the processor manufacturer will also have to shoulder the burden of having to stock and ship multiple versions of a processor bonded with different types of heat sinks.
Thus, a processor card assembly, employing a cover and a thermal plate to form a case, has been developed to house the processor card having the high performance processor mounted thereon. See U.S. patent application Ser. No. 08/723,027, entitled "A processor card assembly including a heat sink attachment plate and an EMI/ESD shielding case". The application has common assignee interest with the present invention.
Additionally, it is also important for a processor card assembly constituted in accordance with the teachings of the above identified U.S. Patent Application to be properly retained, to keep the processor card connected to the receiving connector of the motherboard, notwithstanding a variety of shock and vibration conditions. It is important for these desired retention characteristics to be achieved with a retention apparatus that is simple in design to reduce design and manufacturing cost. It is also important for the engagement of the processor card assembly with the retention apparatus be simple to improve manufacturability.